1. Field of the Invention
The present invention relates to a wireless terminal for dynamically setting communication timing at time slots where sufficient network resources, such as the wireless channel, are available in order to transmit and receive non-real-time data traffic efficiently.
2. Description of the Related Art
Various kinds of data traffic are transmitted and received by wireless data communication terminals, including Web browsing and transmitting/receiving video streamings, e-mails, and large files, etc. Patent Literature 1 and Nonpatent Literature 1 disclose techniques in which the priorities of real-time required data communications are set at higher levels than those for the non real-time data communications, and wireless resources (time, frequency, and power) are preferentially assigned to such high priority data traffic. In these related arts, even data traffic requiring non real-time performance, with lower priority, is assigned with some wireless resources so that data could be exchanged.
In such techniques where priorities and thus the wireless resource are assigned according to the type of data traffic, all the data traffic is always assigned with some wireless resources according to the priority regardless of the condition of the network. Therefore, even when the network is congested, data traffic requiring non real-time performance is assigned with some wireless resources. From the view point of the telecommunications carrier operating the wireless network, this poses a problem in that even less urgent data traffic requiring non real-time performance are assigned with wireless resources even in a congested situation, where these resources are desired to be assigned to other data traffic requiring real-time performance.
From the view point of users of the wireless access network, this also poses a problem where wireless resources that should be assigned to users of applications requiring real-time performance are assigned to users of applications requiring non real-time performance. Such non real-time applications could require so low priority where the exchange of data needs to be completed, for example, in few days or even weeks. In additions, users of applications requiring non real-time performance may demand lower telecommunication fees in exchange for real-time performance.
In order to address these technical problems, the inventors of the present invention have invented and filed a patent application on a system for transmitting and receiving data traffic requiring non real-time performance during a timing, or specifically a vacant time slot, having sufficient wireless resources (see Patent Literature 2).
However, the degree of congestion of wireless resources varies geographically. In addition, there is also a time-oriented tendency with the volume of traffic at wireless networks, for example at access points or base stations. That is, there could be areas where the volume of traffic increases during working hours (e.g. 8 to 19 o' clock) such as at business districts. There could also be areas where the volume of traffic increases after working hours until around midnight such as at residential areas. Therefore, for the users at business districts, the time slot from the middle of the night until the morning, e.g. dawn, is vacant and for the users at residential areas, general working hours could be regarded as vacant or off-peak hours and time slots. Furthermore, these users could move between these two areas. Therefore, the degree of congestion of wireless resources varies depending on the users behaviors and/or geographical situations of base stations, thus it is difficult to fixedly set a time slot, where sufficient wireless resources is available, in advance.
Meanwhile, focusing on the individual users, since each user is likely to repeat his/her behavior on a 24-hour cycle, wireless resources used by these users often reveal the daily variation on a 24-hour cycle similar to the users' behavior. Therefore, it is possible to monitor and/or estimate the degree of congestion of wireless resources considering this periodicity, and the timing of non-real-time communication can be optimized.
Hence, the inventors of the present invention have further invented and filed a patent application of a wireless terminal for use in a system for transmitting and receiving non real-time data traffic during a time slot having sufficient wireless resources, where the wireless terminal is capable of learning the degree of congestion of wireless resources in an autonomous distributed manner based on the call loss rate (percentage of failed connections) or the successful call rate, with consideration of the daily variation of the wireless resource usage. Based on the learned results, the wireless terminal dynamically sets the timing, or the time slot, for the non real-time data to be exchanged (see Patent Literature 3).    Patent Literature 1: Japanese Published Unexamined Patent Application No. 2003-169363    Patent Literature 2: Japanese Patent Application No. 2009-70456    Patent Literature 3: Japanese Patent Application No. 2010-64100    Nonpatent Literature 1: “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 8: Medium Access Control (MAC) Quality of Service Enhancements,” IEEE Std. 802.11e, 2005
Patent Literature 3, however, has the following technical problems.
(1) The timings of data communication, which are distributed according to the degree of congestion, are equally assigned from a time slot with higher level of congestion to a time-slot with a lower level of congestion. Therefore, resulting time slots are not accurately assigned according to the precise degree of congestion.(2) The degree of congestion of wireless resources is represented by the call loss rate. However, it is difficult to accurately represent the degree of congestion of wireless resources only with the call loss rate.(3) The degree of congestion is determined based on the comparison between the call loss rate and a preset threshold value. However, it is difficult to tune the appropriate value of the threshold so that the obtained results represent the degree of congestion accurately. In addition, the time slots having call loss rates exceeding the threshold value are regarded as having the same degree of congestion, which makes it impossible to compare the degree of congestion between such time slots.(4) The period of learning for learning and determining the degree of congestion is preset, and the time slots for data communication to be performed are calculated based on the learned results. In other words, the preset learning period is always required before calculating the time slots of data communication. Therefore, when the condition of the congestion varies in a short period of time, such change of the conditions could not be promptly reflected due to the preset period.(5) Since there are no upper and/or lower limits for the number of communication trials during one time slot, during the assignment of the communication timings from a higher-congestion time slot to a lower-congestion time slot, communication timings may be intensively assigned to some specific time slots. For example, if similar assignments occur in multiple wireless terminals, with the similar condition of the congestion, the time slots with lower-congestion may become congested in the next cycle.